I got the question in my exam and wrote the following and I do not understand what is wrong in it:

Giemsa staining is a staining method to stain particularly malaria and other parasital diseases. G-bands occur because Giemsa stain
consists of A,T rich material i.e. poor gene such that dark and white
bands occur. Each chromosome has an unique reaction to Giemsa staining
so G-bands occur.

0 points. I do not understand what's wrong with it, since in their comments about the same question in my first exam they wrote also the extra questions: What are G-bands? How are they formed and why? This time I answered the given things and got zero mark.

Probably, the mistake was that I did not answer to the question in the scope of medical Biology in some way. However, I am not exactly sure what it is exactly.

How would you answer to the question when you know that the course was about medical biology?

Chromosomes in metaphase can be identified using certain staining techniques, so called banding

(...)

G-bands are most commonly used. They take their name from the Giemsa dye, but can be produced with other dyes. In G-bands, the dark regions tend to be heterochromatic, late-replicating and AT rich. The bright regions tend to be euchromatic, early-replicating and GC rich.

Very well written. - - My attempt of a summary: Staining reveals structural features of the chromosomes in metaphase by banding. Giemsa staining offers better resolution of individual bands of chromosomes along the length of the whole chromosome. It stains DNA to heterochromatic (dark) and euchromatic (white) regions resulting into G-bands, called so because of the dye Giemsa, used in staining historically first, but can be stained also with other dyes. It stains any DNA-containing organism, or, in other words, any known cell. Analysis involves the karyotyping of banded metaphase chromosomes.
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MasiDec 22 '11 at 23:34

Is there any other staining methods for other phases than metaphase of chromosomes? - Is it useful to stain unreplicated daughter chromosomes after metaphase? It is probably harder to do it, since the daughter chromosomes are not in a line, than in staining during metaphase.
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MasiDec 22 '11 at 23:48

1

@Masi in any other phase of the cell cycle, the DNA is much less condensed (called chromatin) and basically all DNA is intermingled, rendering a much more homogeneous staining. You still see regions of condensed chromatin, but it's impossible to identify individual chromosomes. You may do some (very limited) in situ hibridization, but again it's much more informative when cells are in metaphase.
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AleadamDec 23 '11 at 4:13

I need one clarification. Does Giemsa staining of chromosomes stain the DNA and proteins i.e. whole chromosomes? Or does it stain only DNA, not proteins?
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MasiJan 27 '12 at 15:55

It seems that Giemsa staining specifically stains DNA. Sometimes it seems that some proteins are staining but the purpose is not to stain them.
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MasiJan 30 '12 at 17:24